Operational efficiency and output of a gas turbine engine generally increases as the temperature of the hot combustion gas stream increases. High combustion gas stream temperatures, however, may produce higher levels of nitrogen oxides (NOx) and other types of regulated emissions. A balancing act thus exists between operating a gas turbine engine in an efficient temperature range while also ensuring that the output of nitrogen oxides and other types of regulated emissions remain below mandated levels. Lower emission levels of nitrogen oxides and the like may be promoted by providing for good mixing of the fuel stream and the air stream before combustion. Such premixing tends to reduce combustion temperatures and the output of nitrogen oxides. One method of providing such good mixing is through the use of a micro-mixer combustor where the fuel and the air are mixed in a number of micro-mixer tubes positioned within a fuel plenum.
Specifically, a micro-mixer combustor generally includes a fuel plenum with a number of fuel tubes extending through a number of support or assembly plates. Current methods for installing the fuel tubes require precise machining of a number of apertures through the assembly plates. The fuel tubes then may be brazed directly to the assembly plates. Requiring two assembly plates to be prepared and aligned, however, such that the fuel tubes may be brazed properly to both assembly plates may be a manufacturing challenge. This challenge may be further complicated when fuel tube tolerances are taken into account as well as the requirement that not one but multiple fuel tubes must be brazed to a single assembly plate. Such requirements may lead to increased manufacturing costs, stress on the components, and/or inefficient overall operation.
There is thus a desire for an improved micro-mixer fuel plenum and methods for installing fuel tubes therein. Such an improved micro-mixer fuel plenum design may provide fast and efficient fuel tube installation with relaxed overall tolerances.